This gem from the industrial age helps visitors and residents alike traverse hilly Stockholm.

The discovery of an old wall led to the creation of this fascinating museum about the city in the Middle Ages.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

Sweden's "good old days" painstakingly re-created in a model village.

It houses the remains of a 17th-century version of the Titanic.

An enigmatic modern marker left next to a historic Roman site.

An ancient Roman temple first dedicated to an emperor's wife is now a church.

St. Francesca Romana, patron saint of drivers, resides in the church she founded.

This ancient market is often referred to as the oldest shopping mall in the world.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

A Nesting Doll of Churches.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

2300-year-old Roman road connecting the empire.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This crumbling medieval basilica once attracted pilgrims by the thousands to collect a miraculous dust that formed above the saint's tomb.

The ancient latrines of the Greeks, in all their public glory.

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

Ancient serpentine sacrifice holder that has stood the test of time.

This crucial gathering spot along the "hippie trail" still displays old notes between traveling beatniks and backpackers.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

A marvel of Byzantine engineering under the streets of Istanbul.